1. Field of the Invention
The present invention relates to an optical lens system for taking image, and more particularly to an optical lens system for taking image used in a mobile phone camera.
2. Description of the Prior Art
In recent years, with the popularity of the mobile phone camera, the optical lens system for taking image has become thinner and thinner, and the electronic imaging sensor of a general digital camera is typically a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor. Due to advances in semiconductor manufacturing, the pixel size of sensors has been reduced continuously, and miniaturized optical lens systems for taking image have increasingly higher resolution. Therefore, there's increasing demand for image quality.
A conventional high resolution mobile phone camera usually consists of a front aperture stop and four lens elements. U.S. Pat. No. 7,365,920 discloses a four-piece lens assembly, in which the first lens element and the second lens element, which are both glass spherical lens elements, are bonded to each other to form a doublet lens element for eliminating chromatic aberration. However, it suffers from the following disadvantages: the degree of freedom available in the optical system is insufficient since there are too many glass spherical lens elements; and the manufacturing difficulty is increased due to the difficult bonding process of the glass lens elements. U.S. Pat. No. 7,277,238 discloses a lens assembly with four independent lens elements including multiple aspheric lenses, so that the total track length of the optical lens system can be effectively reduced and the image quality can be effectively improved. However, since the aperture stop is located in front of the first lens element, the sensitivity of the optical lens system will be comparatively increased and the production yield of the optical lens system will be difficult to control.
The present invention mitigates and/or obviates the afore-mentioned disadvantages.